The present invention relates to a hydraulic lift device, which is particularly useful for rerailing overturned rail vehicles.
The hydraulic lift device to which the present invention is directed comprises a plurality of hydraulic lift and/or displacement cylinders. A high pressure source communicates with the pressure chamber of each of the hydraulic lift cylinders for driving the piston therein to shift under load, thereby for providing the lift. A low pressure connection to the same pressure chamber feeds a vacuum generator, so that the pressure in the pressure chamber can be reduced to return the unloaded piston. Control valves determine which of the high pressure or low pressure connections is made to the pressure chamber. The operators for the control valves may be provided on a control table.
As noted above, it is contemplated that the hydraulic lift device of the invention be used for rerailing overturned rail vehicles and it is particularly adapted for this purpose. However, hydraulic lift devices are useful in other contexts, as well.
Such a hydraulic lift device has the advantage that for the lift cylinders, it requires only a single hydraulic line and a single three-way control valve which makes it possible to connect the one pressure chamber of the cylinder selectively to the high-pressure connection for lifting or to the vacuum generator, which is for instance a suction nozzle, for returning an unloaded piston. Such a rerailing device with a hydraulic lift device is known from German Federal Republic Pat. No. 1 098 978. Another important advantage is the possibility of particularly sensitive control, especially upon the starting of the lowering of the load. This is inherent because only a single control valve intended for single-acting work cylinders is provided. Devices of this kind are therefore in widespread use.
One disadvantage of these devices is that at temperatures below -20.degree. C., the return motion of the pistons affer elimination of the load is slow, due to the relatively thick consistency of the hydraulic oil.